Transcript Stages of Childbirth

CHAPTER 3
Prenatal
Development
Learning Outcomes
LO1 Describe the key events of the germinal stage.
LO2 Describe the key events of the embryonic stage.
LO3 Describe the key events of the fetal stage.
LO4 Describe environmental influences on prenatal
development, including maternal nutrition,
teratogens, infections, parental drug use,
environmental hazards, and parents’ age.
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TRUTH OR FICTION?
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Newly fertilized egg cells survive without any
nourishment from the mother for more than
a week.
Your heart started beating when you were
only one-forth of an inch long and weighed a
fraction of an ounce.
Parents in wealthy nations have more
children.
The same disease organism or chemical
agent that can do serious damage to a 6week-old embryo may have no effect on a 4month-old fetus.
It is harmless to the embryo and fetus for a
pregnant woman to have a couple of glasses
of wine in the evening.
LO1 The Germinal Stage:
Wanderings
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PRENATAL DEVELOPMENT
• Within 9 months
– A fetus develops from microscopic cell to a neonate
about 20 inches long.
• Normal gestation periods
– 280 days from onset of last menstrual period before
conception
– 266 days from assumed date of fertilization (2
weeks after the beginning of last menstrual cycle)
• Stages of gestation
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Germinal: first 2 weeks
Embryonic: 3rd - 8th week (2 months)
Fetal: 3rd month to birth
Also commonly used is TRIMESTER system
• 3 trimesters = 3 months each
The Germinal Stage: Wanderings
• The period from conception to
implantation
– 36 hours from conception zygote divides
into 2 cells
– Continues dividing on 3-4 day journey to
uterus
– By 72 hours becomes 32 cells
– Mass of dividing cells wanders about the
uterus until finally implanting in uterine wall
– Total time approx. 2 weeks
Figure 3.1 – The Ovarian Cycle, Conception,
and the Early Days of the Germinal Stage
Division of the zygote creates the hollow sphere of
cells termed the blastocyst, which becomes implanted
in the uterine wall.
The Germinal Stage: Wanderings
(1st 2 weeks)
• Terms and concepts:
– Blastocyst
• Fluid filled ball of dividing cells that begin to separate into
groups and eventually become different structures
– Embryonic disk
• Plate-like inner part of blastocyst that becomes the embryo
& fetus
– Trophoblast
• Outer part of blastocyst that becomes 4 different
membranes
– 1 - makes blood cells until liver develops
– 2 - develops the umbilical cord and placenta
– 3 - develops into amniotic sac
– 4 - becomes the chorion that lines the placenta
The Germinal Stage: Wanderings
(1st 2 weeks)
• Terms and concepts, con’t.
– Umbilical Cord
• The tube that connects the developing fetus to the
placenta
– Placenta
• Organ connected to uterine wall and fetus by the
umbilical cord. Serves as relay station between mother
and fetus for exchange of nutrients and wastes.
– Implantation Bleeding
• May be caused when small blood vessels lining the
uterus are ruptured during implanting process
• Most women experiencing this have normal pregnancy
– Miscarriage
• Usually stems from abnormalities in development
process
• Nearly 1/3 of pregnancies end in miscarriages, most
within first 3 months
LO2 The Embryonic Stage
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The Embryonic Stage
• The embryonic stage begins with implantation
and covers the first 2 months.
• Characterized by major organ development
following:
– Cephalocaudal trend:
• From head to tail
– Proximodistal trend:
• From near to far
– Early brain and organs near spine allows them to
play key roles in further development
• Growth of head takes precedence
• Organ systems near spine grow prior to the extremities
Figure 3.2 – A Human Embryo at 7 Weeks
Note that the head is oversized in relation to the rest
of the body.
© Petit Format/Nestle/Science Source/Photo Researchers
The Embryonic Stage (3-8 weeks)
• Terms and concepts:
– Ectoderm
• Outer layer of embryonic disk cells develop into:
– Nervous system, sensory organs, nails, hair, teeth, outer
layer of skin
– Neural tube
• Two ridges in the blastocyst fold and form a tube
– This will become the nervous system.
– Endoderm
• Inner layer of the embryo develops into:
– Digestive and respiratory systems, liver, pancreas
– Mesoderm
• Middle layer of embryo develops into:
– Excretory, reproductive, and circulatory systems; and the
muscles, skeleton, and inner layer of skin
The Embryonic Stage (3-6 weeks)
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Time frame developments:
– 3rd week:
• Head and blood vessels begin to form
– 4th week:
• Arm and leg buds begin to appear
• Eyes, ears, nose, and mouth start to shape
• Nervous system/brain begins developing
– 5-6 weeks:
• Embryo about 1/4 - 1/2 inch long
• Heart begins to beat
• Both internal and external genitals resemble female structures
– 6-8 weeks:
• Head rounded and distinct facial features appear
• 7th week genetic XX or XY codes causing sex organs to
differentiate
• Hands and feet (initially with webbed toes and fingers, but
separate by end of 8th week)
• Teeth buds form; kidneys begin filtering blood; liver starts to
produce blood cells
• Embryo is approx. 1 inch long and weighs about 1.30th ounce
The Embryonic Stage (6-8 weeks)
• Time frame developments:
– 6-8 weeks:
• Head rounded and distinct facial features appear
• 7th week genetic XX or XY codes causing sex organs to
differentiate
• Hands and feet (initially with webbed toes and fingers, but
separate by end of 8th week)
• Teeth buds form; kidneys begin filtering blood; liver starts
to produce blood cells
• Embryo is approx. 1 inch long and weighs about 1.30th
ounce
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LO3 The Fetal Stage
© Tetra Images/Jupiterimages
• This final stage in gestation lasts from the start of the
3rd month (9 weeks) until birth
• 1st trimester - 9-12 wks (3 mos):
– Major organ systems formed
– Begins to turn and respond to external stimulation
– Fingers and toes fully formed
– Eyes and sex can be clearly seen
© Claude Edelmann/Photo Researchers, Inc. /© Don Wilkie/iStockphoto.com /© graham klotz/iStockphoto.com
The Fetal Stage (9weeks/3mos - Birth)
The Fetal Stage (9weeks/3mos - Birth)
• 2nd trimester - 13-24 wks (6 mos):
– Dramatic gains in size - from 1 oz. to 2 lbs. and 3
inches to 14 inches
– Opens and shuts eyes, sucks thumb, sleep/wakes,
perceives light and sound
– Downy hair growth
• 3rd trimester - 25-36 wks (9 mos):
– Organs continue to mature
– Gains about 5.5 lbs and doubles in length
– At 7th month nearly doubles weight and grows
another 2 inches
– Chances of survival if born now nearly 90% - at 8
mos. Odds overwhelmingly in favor
– Newborn boys avg. 7.5 lbs. Girls avg. 7 lbs.
Fetal Perception
• By week 13, fetus responds to sound.
• During 3rd trimester, fetus discriminates to
differences in pitch.
– Exhibiting variety in movement and changes in
heart rate
• DeCasper & Fifer experiment (1980)
– Newborns exhibit preference for readings of
mother during final month and half of pregnancy
• Fetal learning may be one basis for
developing attachment to mother.
Fetal Movements
• First fetal movements felt by mid-4th month
• 2/30 weeks fetus becomes very active
– Turning somersaults clearly felt by mother
– No danger of umbilical cord breaking or wrapping
around fetus at this time
• Different patterns of prenatal activity
– 5-6 months
• Slow squirming movements
• Also sharp jabbing and kicking about same time
• Growth eventually causes fetus to become
cramped for space
– Activity becomes markedly less active during the
final month of gestation
Birth Rates around the World
• U.S. Census Bureau “guesstimates” pre-history
populations
– 10,000 years ago: 5 million humans
– 5,000 years ago: 14 million
• Year 1
– 170 million
– 1.7 billion
• 1950
– 2.5 billion
• Today
– Approx. 6.5 billion
• Population explosion relative to location on planet
© Christine Osborne Pictures/Alamy
• 1900
LO4 Environmental Influences
on Prenatal Development
© Tetra Images/Jupiterimages
Environmental Influences on Prenatal
Development
• The developing fetus is subject to many
environmental hazards:
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Nutrition
Teratogens
Critical Periods of Vulnerability
Sexually Transmitted Infections
Rubella
Toxemia
Rh Incompatibility
Drugs Taken by the Parents
Other unknown hazards
Age of parents
Nutritional Hazards
• Maternal malnutrition
– Linked to low birth weight, premature birth,
retardation, cognitive deficiencies,
behavioral problems, and cardiovascular
disease
– Misconception that fetus can “take what it
needs”
– Effects of fetal malnutrition
• May sometimes be counteracted by a
supportive, care-giving environment
• Enriched daycare programs show
improved intellectual and social skills by
age 5
Nutritional Hazards
• Maternal obesity
• Linked with higher risk of stillbirth and neural
tube defects
• Typical weight gain
– Without restricting diet, normal weight gain is 25-35
lbs.
– .05 lbs. pr wk during 1st half of pregnancy & 1 lb.
per wk. thereafter is desirable
– Sudden large gains or losses should be discussed
with doctor
Teratogens
• Environmental agents that can harm the
embryo or fetus:
– Drugs
• Alcohol and other drugs
– Substances produced by the mother’s body
• Rh-positive antibodies
– Heavy metals
• Lead and mercury
– Hormones
• Healthful in many ways, but harmful if in excess
– Radiation
• X-rays; nuclear bombs
– Disease-causing organisms (pathogens)
• Bacteria and viruses
Critical Periods of Vulnerability
• Exposure to certain teratogens is most
harmful during critical periods that
correspond to times when certain organs
are developing
• Major organs differentiate during
Embryonic Stage making an embryo
generally more vulnerable than a fetus
Figure 3.3 – Critical Periods in Prenatal
Development
Sexually Transmitted Infections (1)
• Syphilis can cause:
– Miscarriage, stillbirth, congenital syphilis
(present at birth)
– Detected with early routine blood tests
– Treated with antibiotics
– Fetus will probably not contract if treated
before 4th month of pregnancy
– If left untreated:
• Fetus may be infected in utero and develop
congenital syphilis
• Approx. 12% of those infected die
Sexually Transmitted Infections (2)
• HIV/AIDS
– Disables body’s immune system leaving victims
prey to a variety of fatal illnesses
– Lethal unless treated with antiviral drugs; treatment
not guaranteed
– Transmitted by sexual relations, blood transfusions,
sharing hypodermic needles, childbirth, breast
feeding
– 1/4 of babies born to HIV-infected mothers are
infected also
• Due to rupture of blood vessels during childbirth
• HIV also found in breast milk; transmission of HIV affects
about 1-6 (16.2%)
RUBELLA (a.k.a. German Measles)
• A viral infection
• 20% chance of birth defects if infected during
first 20 weeks of pregnancy
– Deafness, mental retardation, heart disease, blindness
• Most adult women had rubella as children
which offers immunity.
• Vaccination can be done during pregnancy but
best done prior.
• Inoculations have resulted in dramatic decline
of birth defects from Rubella.
– 1964-65 = 2,000 CASES
– 2001 = 21
Toxemia
• Life threatening disease related to
maternal deaths
– High blood pressure in late 2nd or early 3rd
trimester
– Often causes premature birth or undersize
babies
– Linked to malnutrition but causes are
unclear
– Women not receiving adequate prenatal
care are more susceptible.
Rh Incompatibility
• Rh is a blood protein found in red blood cells of
some individuals.
• Rh Incompatibility occurs when:
– Mother is Rh-neg and fetus is Rh-pos (can get pos.
cells from father)
• The neg./pos. combo occurs in approx. 10% of
U.S. couples.
• If antibodies enter fetal bloodstream:
– Can cause anemia, mental deficiency, death
– Fetus or newborn at risk can receive a blood
transfusion to remove the mother’s antibodies.
Drugs taken by Parents (1)
• All medications (even OTC meds like aspirin)
can be potentially harmful to a fetus.
– Always seek medical advice before taking ANY
meds.
• Some common drug problems:
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Thalidomide
- Caffeine
Hormones
- Cigarettes
Vitamins
Heroin and Methadone
Marijuana
Cocaine
Alcohol
Drugs taken by Parents (2)
• THALIDOMIDE
– Marketed in 1960s for treating insomnia and
nausea; used to alleviate “morning sickness”
– Available in Germany and England without Rx
– Within a few years, more than 10,000 babies
were born with severe birth defects.
• Missing and malformed/stunted arms and legs
– A dramatic example of critical periods to
teratogens
Drugs taken by Parents (3)
• HORMONES
– Women at risk of miscarriage may be prescribed
hormones to help maintain pregnancy.
– PROGESTIN
• Similar to male sex hormones; can masculinize external
sex organs of female embryos
– DES
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Powerful estrogen
Given to many women in 1940-50s to prevent miscarriages
Causes cervical and testicular cancer in some offspring
1 in 1,000 daughters of DES users develop cancer in
reproductive organs
• Also more likely to have premature and low birth weight
babies
• Both daughters and sons of users have high rates of
infertility and immune system disorders.
Drugs taken by Parents (4)
• VITAMINS
– Normal use of multivitamins for mothers
pose no threat and are often prescribed.
– High doses of Vitamins A and D have
however been associated with:
–CNS damage
–Small head size
–Heart defects
Drugs taken by Parents (5)
• HEROIN & METHADONE
– Easily cross the placental membrane
– Fetuses of regular users can become
addicted in utero.
– Linked to low birth weight, premature birth,
and toxemia
– Treatment of addicted newborns includes:
• Administering drug shortly after birth to prevent
withdrawal; then gradually weaned from drug
• May have behavioral effects - motor and
language delays at 1 year of age
Drugs taken by Parents (6)
– Risks for fetus and child
• Slow growth rate
• Babies exhibit tremors, startling (CNS
impairment)
• Cognitive effects
– Mixed findings in studies; none conclusive
– Some suggest problems with learning and
memory
– Also increase in hyperactivity, impulsivity,
short attention spans, increase in
delinquency and aggression
– Overall reflects impairment in functioning in
school and conforming to social norms
© Julie Masson Deshaies/iStockphoto.com
• MARIJUANA
Drugs taken by Parents (7)
• COCAINE
– Increases risk of stillbirth, low birth weight,
and birth defects
– Infants often excitable and irritable or
lethargic and sleep disturbed
– Delays in cognitive development seen at 1
year
– Also show problems at later ages with lower
receptive and expressive language skills
Drugs taken by Parents (8)
• ALCOHOL
– Even moderate drinking can place a fetus at
risk for serious birth defects and increase
risk for miscarriages
– Heavy drinkers place fetus at risk for
FETAL ALCOHOL SYNDROME (FAS)
• PHYSICAL SYMPTOMS
– Smaller size and brains; distinct facial features include
wide set eyes, flat nose, underdeveloped upper jaw,
malformed limbs, poor coordination, heart problems
• PSYCHOLOGICAL CHARACTERISTICS
– Retardation, hyperactivity, distractibility, less verbal
fluency, learning disabilities
• MALADAPTIVE BEHAVIORS
– Poor judgment, poor perception of social cues
Figure 3.4 – Fetal Alcohol Syndrome (FAS)
© George Steinmetz
Other Unknown Hazards
• Unknown exposure to other environmental
hazards: a.k.a. pollution
• HEAVY METALS
– Lead, Mercury, Zinc
– Can delay mental development at ages 1 & 2 years
• PCB’s (industrial product waste found in water)
– Smaller babies, poorer motor functioning, memory
deficits
• RADIATION
– Damage to eyes, CNS, and skeleton
– Results of WWII bombing of Japan saw high
incidence of birth defects and mental retardation
• Father’s exposure can also effect child
Age of Parents
• Ideal age for childbearing = 20s
– Teen Mothers
• Higher incident of infant mortality, low birth weight
• Not adequately mature physically for stress of preg.
• Less educated and less likely to get prenatal care
– Older Mothers
• Fertility declines gradually until mid-30s then accelerates;
after mid-30s reproductive system does not function as
efficiently
• After 30-40s see increase in stillborns and preterms
• With adequate care, risk is lessened
– Older Fathers: more likely to produce abnormal sperm